This invention relates generally to piezoelectric devices and, more particularly, to an apparatus and method for providing temperature compensation of a piezoelectric device to vary its operating characteristics in response to changes in temperature proximate the device.
Piezoelectric devices alter their shape in response to an applied electric field. An electric field applied in the direction of polarization effects an expansion of the piezoelectric material in the same direction, while a voltage applied in the opposite direction of polarization will cause a contraction of the material in that same direction. Piezoelectric bending actuators, such as thermally pre-stressed bending actuators, use the xe2x80x9cbendingxe2x80x9d action of the actuator to convert electrical energy into mechanical energy. Several different high performance bending devices or actuators have been developed, such as those disclosed in U.S. Pat. Nos. 5,471,721 and 5,632,841 to which the reader is referred.
Due to the nature of their construction, however, the performance of piezoelectric devices is temperature dependent and presents a problem in applications having a broad range of operating temperatures, such as 0xc2x0 C. to 100xc2x0 C., for example. In this and other wide temperature ranges, piezoelectric devices may have force and displacement characteristics that change in response to changes in temperature of the device. Thus, a piezoelectric device that has a given axial displacement at one temperature may have a different displacement at a different temperature.
In response to an applied voltage, the piezoelectric device will change in shape by a predetermined axial displacement and apply a predetermined force or load at that temperature. However, these characteristics will also change at a different temperature of the piezoelectric device. Therefore, the piezoelectric device should be temperature compensated to provide a consistent, reliable and predictable movement or displacement and force in response to an applied voltage over a broad temperature range.
In the past, piezoelectric devices have been temperature compensated by mechanical means, such as by hydraulic and mechanical compensation, and by special compensating materials. However, these compensating methods can add cost and complexity, and increase the overall size of the piezoelectric device.
While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
A clamping device provides temperature compensation of a piezoelectric device having first and second opposed surfaces and a peripheral edge extending therebetween. The clamping device is configured to engage the first and second opposed surfaces of the piezoelectric device proximate the peripheral edge, and is operable to apply a variable clamping force to the piezoelectric device. A temperature responsive device is coupled with the clamping device and is operable to vary the applied clamping force in response to changes in temperature proximate the piezoelectric device. The variable clamping force alters operating characteristics of the piezoelectric device to provide temperature compensation of the piezoelectric device.